The present invention relates to power operated stock advancing apparatus of the type having a swingably mounted control arm for sensing the size of a loop of stock between the stock advancing apparatus and a stock processing machine and for controlling operation of a drive motor for the stock advancing apparatus in a manner to maintain a loop of stock between the stock advancing apparatus and the processing machine. The stock advancing apparatus may comprise a stock reel that effects advance of the stock by winding or unwinding stock from a coil. The stock advancing apparatus can also comprise powered stock feed rollers or powered stock straightening rollers. Some stock advancing apparatus such as disclosed in U.S. Pat. No. 4,555,071 provide a cam on the dancer arm shaft that actuates a switch to start and stop the drive motor for the stock advancing apparatus to maintain a loop in the stock. Stock advancing apparatus have also heretofore been made as disclosed in U.S. Pat. No. 4,578,621 in which the dancer arm operates a speed control potentiometer to produce a variable control voltage correlative with the angular position of the dancer arm to increase and decrease the speed of the stock advancing apparatus in a manner to maintain a loop in the stock between the stock advancing apparatus and the subsequent stock processing machine.
In many stock processing machines such as punch presses and the like, the stock is moved in step fashion through the stock processing machine to provide a dwell time for the machine to operate on the stock. This stepped movement of the stock through the stock processing machine produces relatively rapid changes in the size of the stock loop and the dancer arm moves angularly with changes in size of the stock loop. The dancer arm is commonly counterbalanced to adjust the force exerted by the stock loop sensing arm on the stock, and adapt the apparatus for different types and weights of stock. In practice, the dancer arm not only moves up or down with changes in the size of the stock loop caused by the stepped advance of the stock through the processing machine, but also sometimes bounces out of contact with the stock, particularly at high operating speeds and when the arm is counterbalanced to apply only a light force on the stock in the loop. Bouncing of the control arm on the stock loop can not only cause excessive cycling of the drive motor for the stock advancing mechanism but can also adversely affect control of the size of the stock loop.
It has heretofore been proposed to attach a spring or a fluid type shock absorber to the stock loop control arm at a location spaced from its pivot axis to control bouncing of the stock loop control arm. However, it is common practice in dancer arm controlled stock advancing apparatus to adjust the operating angle of the stock loop control arm as well as the length of the stock loop control arm and the counterbalancing of a stock loop control arm to accommodate different types and weights of stock, and a spring or fluid type shock absorber attached to the stock loop control arm is not readily adjustable to accommodate the various different control arm adjustments and to effect different control arm dampening action for different operations.